Machine tool

ABSTRACT

To improve a machine tool, comprising a machine frame, a workpiece holder arranged on the machine frame for a workpiece to be machined, a tool holder arranged on the machine frame for receiving a tool and at least one drive with a slide for executing a relative movement between the tool and the workpiece in the direction of at least one axis, such that it allows as high dynamics as possible, it is proposed that the drive comprise electric linear motors aligned parallel to the axis and spaced from one another in a transverse direction, that the slide extend between the two linear motors, and that a control be provided for simultaneously operating the linear motors for displacement of the slide.

This application is a continuation of commonly assigned, U.S. patentapplication Ser. No. 08/055,686 filed Apr. 29, 1993, abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a machine tool comprising a machine frame, aworkpiece holder arranged on the machine frame for a workpiece to bemachined, a tool holder arranged on the machine frame for receiving atool and at least one drive with a slide for executing a relativemovement between the tool and the workpiece in the direction of at leastone axis.

In the machine tools known so far, the drive comprises, as a rule, amotor which rotatingly drives a spindle with a spindle nut for executinga relative movement along the axis.

With such a rotating drive, the dynamics are limited on account of therotational speed possible for the drive motor and the spindle.

The object underlying the invention is, therefore, to so improve amachine tool of the generic kind that it allows as high dynamics aspossible.

SUMMARY OF THE INVENTION

This object is accomplished in accordance with the invention with amachine tool of the kind described at the beginning by the drivecomprising two electric linear motors aligned parallel to the axis andspaced from one another in a transverse direction, by the slideextending between the two linear motors, and by a control being providedfor simultaneously operating the linear motors for displacement of theslide.

With the inventive concept of using two linear motors aligned parallelto the axis and simultaneously employed to displace the slide, highdynamics are achievable for driving the slide because the limitationsusually prevailing with rotating spindle drives no longer exist.Furthermore, the problems with play, elasticity, friction and wear whichcommonly occur with the known spindle drives are eliminated.

Special advantages apart from the high acceleration and the high speedsare large displacement paths and exact positioning.

The use of two simultaneously operated linear motors offers additionaladvantages because these provide in a simple way particularly highacceleration forces for highly dynamic movement of the slide.

The two linear motors can be operated in many different ways.

One advantageous solution provides the possibility of operating the twolinear motors jointly as a single NC-axis. However, in spite of thejoint activation as NC-axis, it is advantageous for separate powersupplies to be provided. As far as control technology is concerned, thispossibility can be implemented at reasonable cost.

As an alternative to this, provision is made for the two linear motorsto be activatable as NC-axes independently of one another. This meansthat each of the linear motors has an NC-axis-control of its own and apower supply of its own. This has the advantage that the movements ofthe two linear motors can be attuned better to one another.

This is possible in a particularly advantageous way when each linearmotor has a position measuring system of its own associated with it.

In particular, parallel displacement of the slide is then achievable byactive control of the linear motors so that there are essentially nomore transverse forces acting on guides of the slide to cause tilting ofthe slide.

The linear motors can be constructed in many different ways. It isexpedient for single-cam linear motors to be used.

In a preferred solution, the linear motors comprise primary andsecondary parts aligned parallel to a plane as linear motor parts.

A particularly compact construction is obtained with the use of suchlinear motors when the plane in which the linear motor parts extend runstransverse to the transverse direction.

To enable the heat of the linear motors to be conducted away well, itis, furthermore, advantageous for the linear motors to be respectivelyarranged on both sides and in outer regions of the slide and a slidesupport.

The arrangement of the linear motors is particularly advantageous whenthese are arranged at respective opposite outer sides of the slidesupport or the slide. This solution enables optimum removal of the heatgenerated by the linear motors into the environment and, at the sametime, a slide or slide support design which is as compact as possible inthe direction of the respective axis.

In the explanation of the embodiments so far, the guidance of the slidewas not described in further detail. It is, for example, conceivable toguide the slide on a main guide. However, it is particularlyadvantageous, especially for the accuracy and exactness of the guidanceof the slide, for the slide to be guided on two main guides extending inparallel spaced relation to one another.

To obtain a compact design and, on the other hand, as explained above,to provide the possibility for optimum cooling of the linear motors,provision is advantageously made for the main guides to be arrangedbetween the linear motors.

With this external arrangement of the linear motors with respect to themain guides, stability problems could arise on account of the forcesacting between the linear motor parts.

These stability problems are advantageously solved by the respectivelinear motors lying between a main guide and an additional guide,respectively, with the two guides acting between the slide and therespective slide support. The provision of the additional guides thusenables stable guidance of the linear motor parts relative to oneanother and sufficient rigidity with as small a mass as possible ofslide and slide support and hence high dynamics.

To achieve optimum cooling, provision is preferably made for the linearmotors to comprise cooled primary and secondary parts.

Such cooling can be carried out in many different ways. One embodimentpreferably makes provision for the cooling of the primary and secondaryparts to be carried out by cooling channels in holding elements for theprimary and secondary parts so that these are coolable by direct contactwith the holding elements respectively carrying the cooling channels.

A coolant which is coolable to a defined temperature by a cooling devicepreferably flows through the cooling channels.

In the explanation of the embodiments so far, it was merely explainedhow optimum dynamics of the slide are achievable. With the use ofelectric linear motors both acceleration and braking are possible withthese linear motors.

In spite of this, it is advantageous, especially for safety reasons, forthe slide to be additionally fixable by a braking device.

The braking device is preferably designed as a mechanically actingbraking device. In particular, the braking device serves as automaticbraking device to automatically brake the slide when predeterminablepositions of the slide are reached.

Provision is preferably made for the braking device to be actuatable byan end position switch which thus brakes and fixes the slideindependently of the activation of the linear motors when an endposition fixed by the end position switch is reached.

As an alternative or supplement to this, provision is advantageouslymade for the braking device to be provided as a safety device in theevent of failure or an emergency stop.

The braking device is then preferably actuatable by a failure switch oremergency stop switch so that in the event of failure of the electricpower supply for the linear motors or actuation of an emergency stopswitch, the braking device brakes and fixes the slide.

It is particularly expedient, especially for effectively applying ashigh braking forces as possible, for the slide to be fixable by twobraking devices spaced from one another in the transverse direction. Inparticular, effective braking of the slide is thus possible and abruptbraking thereof is avoided.

In the description of the embodiments so far, the design of the slidesupport was not described in further detail. In an embodiment which isadvantageous particularly with respect to its stability and resistanceto distortion, provision is made for the slide support to be designed asa yoke.

The slide support can, for its part, be part of a slide which is movablerelative to the machine frame or it can be part of the machine frame. Inthis case, provision is preferably made for the slide support designedas a yoke to form a stand of the machine frame which is seated on amachine bed.

In an advantageous embodiment of an inventive machine tool, provision ismade for the tool holder to be held on a slide displaceable in onedirection, and for, in particular, the workpiece holder to be held on aslide displaceable in another direction transverse to the one direction.

The workpiece holder is preferably rotatable by a rotary drive about anaxis relative to the machine frame so that the workpiece can be broughtinto various rotary positions about an axis of rotation or made toexecute a rotary movement--for example, in the fashion of aspindle--about this axis.

A particularly expedient solution makes provision for the rotary driveto be designed as an NC-axis so that rotary movements about preciselydeterminable angles or also rotary machinings can be carried out.

It is particularly advantageous for the rotary drive to comprise adirect drive, i.e., for there to be no gearing connected between a drivemotor and the workpiece holder.

The advantages of such a direct drive are to be seen in the eliminationof gear problems such as play, friction, etc. and the achievable highdynamics.

In combination with a direct drive, the providing of the rotary drivewith a direct measuring system for detecting the rotary positions of theworkpiece holder represents a particularly preferred solution as far asthe thus achievable precision is concerned.

To enable exact positioning and fixing of the workpiece holder inindividual rotary positions, provision is preferably made for the rotarydrive to comprise a braking device for fixing the workpiece holder formachining of the workpiece in each rotary position.

It is preferable--particularly when the machine tool is designed as amachining center--for the rotary drive to be designed as a rotary tablewith which the workpiece holder is rotatable about a vertical axis.

The workpiece holder is preferably fixable in and releasable from asupport on the rotary table so that the workpiece is fixed together withthe workpiece holder on the rotary table, machined and then transportedfurther together with the workpiece holder.

The workpiece holder is preferably hydraulically clampable in thesupport on the rotary table.

It is preferable for the workpiece holder to be designed as a pallet onwhich the workpiece is clamped.

Particularly in the case of a rotary table rotatable about a verticalaxis, provision is preferably made for this rotary table to sit on aslide which, for its part, is displaceable on a longitudinal bed of themachine frame comprising a slide support.

So far, no further details have been given about the arrangement of thetool. It is, for example, conceivable to arrange a stationary tool onthe slide and perform, for example, rotary machining with the tool.

As an alternative to this, it is conceivable, particularly when theinventive machine tool is a machining center, for a tool spindle forreceiving the tool to be arranged on the slide and for the tool to thusbe a rotatingly driven tool.

In this case, the tool spindle is preferably arranged on the slide suchthat it extends through a central opening of the slide support designedas a yoke. If this slide support is, in turn, part of a slide and guidedon a further slide support which is designed as a yoke, provision isthen advantageously made for the tool spindle to extend through thecentral openings of both yokes.

An advantageous version of an inventive machine tool comprises, inparticular, a first slide which is movable along a first axis and isguided on a first slide support. This slide support is, in turn, part ofa slide which is displaceable along a second axis transversely to thefirst axis and is, for its part, guided on a second slide support. Thissecond slide support is part of the machine frame and is seated, inparticular, in the form of a stand, on a machine bed.

A third axis extending transversely to the first and second axes isformed by a slide displaceable along a longitudinal bed carried by themachine bed. This division of the axes allows optimum stability and, inparticular with linear drives, optimum distribution of the masses inorder to obtain as high dynamics as possible with all axes.

The longitudinal bed is preferably encompassed by the machine bed.

A particularly stable construction is obtained when two Y-shaped legsadjoin the longitudinal bed and the legs are connected to the stand attheir ends which face away from the longitudinal bed.

In a further inventive embodiment, provision is made for a work area ofthe machine tool to be enclosed by a cell.

To allow highly dynamic movement of the slide, provision is made for adelimitation of the cell to be formed by at least one shield held on theslide and extending away from the latter in its direction of movement,with the shield reaching in all the axis positions of the slide in thedirection in which it extends at least as far as a delimitation of thework area in the direction in which it extends.

It is particularly advantageous for the delimitation of the cell to beformed by two shields extending in opposite directions.

In the case of a double-slide system, provision is preferably made for atool or workpiece holder carried by a second slide to extend through amovement gap between these two shields.

To enable optimum covering of this movement gap in a way suitable forhighly dynamic movements, provision is preferably made for it to also becovered at least in one direction by a shield movable by the slide.

This shield can be guided in any chosen way. It is preferable for theshield to be guided by longitudinal guides on both sides of the movementgap.

In the case of a compound slide system, a particularly advantageousembodiment of an inventive machine tool makes provision for two shieldsextending in opposite directions to be provided on one compound slideand for a shield extending in one direction to be provided on the othercompound slide, with a telescope-type cover arranged in the otherdirection, and for the shields and the telescope-type cover to form adelimitation of the cell.

So far, no further details were given about the design of the shields.To achieve good stability, a shield is designed as light-weight buildingpanel comprising a front and a rear metal sheet and between these areinforcement element with cavities therein.

It is expedient for the reinforcement element to be a corrugated metalsheet. It is, however, also conceivable for it to be in the form of ahoneycomb structure, etc.

A solution in which the front and rear sheets are made of aluminum isparticularly advantageous. It is even better for the reinforcementelement to also be made of aluminum and it is preferable for thereinforcement element and the sheets to be adhesively connected to oneanother.

A further advantageous embodiment comprises a tool magazine arrangedoutside of the cell.

The tool magazine is preferably in the form of a magazine wheel withtool receptacles along its circumference.

To enable tool exchange with the tool holder as simply and as quickly aspossible, provision is made in the case of a cell surrounding the workarea, for a side wall to be provided with a swing door.

This swing door is preferably designed as a double-swing door with twodoor leaves.

The door leaves can be opened in any chosen way. Since very quick entrythrough the double-swing door requires as quick opening of the two doorleaves as possible, provision is preferably made for the door leaves tobe adapted to be brought into an open position by being acted upon bythe tool holder.

For this purpose, damping elements are preferably provided on the doorleaves to reduce the forces of acceleration applied to the door leavesby the tool holder.

To bring the door leaves back into their closed position again and keepthem in it in as simple a way as possible, provision is preferably madefor the door leaves to be acted upon by spring elements in the directionof their closed position.

Since very quick opening of the two door leaves involves the danger ofthese springing back from their open position when they strike a stop,provision is preferably made for each door leaf to be provided with abraking device, preferably in the form of a friction braking device,which brakes the free movability of the door leaves.

Further features and advantages of the inventive solution are thesubject matter of the following description and the appended drawings ofseveral embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective overall view of a machine tool according to theinvention;

FIG. 2 a plan view in the direction of arrow A in FIG. 1;

FIG. 3 a plan view in the direction of arrow B in FIG. 1;

FIG. 4 a plan view in the direction of arrow C in FIG. 1;

FIG. 5 a section through a Z-slide with a rotary drive;

FIG. 6 a perspective illustration of a second embodiment;

FIG. 7 a partial sectional illustration taken along line 7--7 in FIG. 6;

FIG. 8 a partial sectional illustration taken along line 8--8 in FIG. 6;and

FIG. 9 a partial sectional illustration taken along line 9--9 in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of an inventive machine tool illustrated in FIG. 1comprises a machine frame designated in its entirety 10 on which aworkpiece 12 is positionable. For machining the workpiece 12 with a tool14, the tool 14 is held in a tool spindle 16 which, for its part, isdisplaceable in an X- and a Y-direction on the machine frame 10. Theworkpiece 12 is also movable in a Z-direction relative to the toolspindle 16 and perpendicular to the X- and Y-axes so that, in all, theworkpiece 12 and the tool 14 are movable along three axes extendingperpendicular to one another, namely the X-, Y- and Z-axes, formachining the workpiece 12.

To enable movement of the tool spindle 16 along the X- and Y-axes, thetool spindle 16 is held on a Y-slide 18 which, for its part, isdisplaceable on a slide support 20, designed as a yoke with a centralopening 22, in the Y-direction. The tool spindle 16 extends with arearward section 24 facing away from the tool 14 (FIGS. 2 and 3) throughthe central opening 22. The central opening 22 is, therefore, designedsuch that the tool spindle 16 is movable along its maximum Y-path ofdisplacement, predetermined by the movability of the Y-slide 18 relativeto the slide support 20, in an unimpeded way without colliding with rimsof the central opening 22.

The slide support 20 is encompassed by an X-slide 26 which, for itspart, is held on a stand 28 for displacement along the X-axis. The stand28 is also designed as a yoke and has a central opening 30 through whichthe rearward part of the tool spindle 24 extends, with the centralopening 30 being designed such that the tool spindle 16 is movabletherein in a collision-free manner in all possible positions along theX- and Y-axes.

The stand 28 sits as part of the main frame 10 on a machine bed 32 whichis likewise encompassed by the machine frame 10. The machine bed 32comprises a longitudinal bed 34 which extends parallel to the Z-axis andhence perpendicular to a plane spanned by the X-axis and the Y-axis awayfrom the stand 28. For stable connection of the stand 28 to thelongitudinal bed 34, the machine bed 32 has two legs 36 protruding inY-shaped configuration from the longitudinal bed, with the stand 28seated on the ends 38 of the legs 36 that face away from thelongitudinal bed 34 and the ends 38 lying below vertical yoke beams 40of the stand 28.

Guided on the longitudinal bed 34 parallel to the Z-axis is a Z-slide 42which carries a rotary drive 44 with which the workpiece is rotatableabout a B-axis.

The rotary drive 44 forms together with a support 46 for a workpieceholder 48 a rotary table designated in its entirety 50 for the workpieceholder 48 which is preferably designed as a pallet for holding theworkpiece 12.

The B-axis lies parallel to the plane spanned by the X- and Y-axes andpreferably extends perpendicular to a spindle axis 52 of the toolspindle 16.

As illustrated in FIGS. 2 and 3, the Y-slide 18 includes a bridge 70which carries the tool spindle 16. The bridge 70 carries on a rear side72 guide carriages 74 and 76 which are guided on guide rails 80 and 82spaced from one another on a front side 78 of the slide support 20 andextending parallel to the Y-axis. The guide carriages 74 and 76 formwith the guide rails 80 and 82 main guides 84 and 86 for the Y-slide 18which are preferably arranged symmetrically with the spindle axis 52.

Linear motors 88 and 90, respectively, are arranged beside the mainguides 84 and 86, respectively, more particularly, on the sides facingaway from the tool spindle 16. Both of these serve jointly to displacethe Y-slide 18 in the direction of the Y-axis and to do so are operatedsimultaneously.

The two linear motors 88 and 90 are each arranged at the side of theslide support 20, more particularly, in such a way that they lie besidea side face 92 and 94, respectively, of the slide support 20 and extendwith their winding planes 96 parallel to the Y-direction and parallel tothe Z-direction.

Each of the linear motors includes a primary part 98 which is mounted ona holding flange 100 of the Y-slide 18 on a side facing the side face 92and 94, respectively. The holding flange 100 extends from an outer end102 of the bridge 70 approximately parallel to the side face 94 andoverlaps it.

A secondary part 106 is arranged by means of a supporting element 104 onthe slide support 20 facing the primary part 98. The secondary part 106is seated on the supporting element 104 on a side facing the holdingflange 100, and the supporting element 104 is held on the side face 94.

To support the holding flange 100 against the forces acting between theprimary part 98 and the secondary part 106 perpendicular to the windingplane 96, the holding flange 100 is guided on its side facing away fromthe bridge 70 by an additional guide 108 which comprises a guidecarriage 110 connected to the holding flange 100 and a longitudinalguide 112 seated on the side face 94 and extending parallel to theY-axis. This additional guide 108 thus guides the holding flange 100precisely in defined alignment with the side face 94 of the slidesupport 20 and hence the primary part 98 at a defined spacing from thesecondary part 106, more particularly, jointly with the main guides 84and 86.

For cooling the primary part 98 and the secondary part 106 of each ofthe linear motors 88 and 90, cooling channels 114 and 116, respectively,are provided in the holding elements for these, i.e., in the holdingflange 100 for the primary part 98 and in the supporting element 104 forthe secondary part 106 so that both the primary part 98 and thesecondary part 106 are coolable by the holding element respectivelycarrying these, i.e., the holding flange 100 and the supporting element104. A coolant which is cooled down to a defined temperature by acooling device flows through these cooling channels 114 and 116.

The two linear motors 88 and 90 are activated by a common control 118provided for both linear motors 88 and 90 and constituting an NC-axiscontrol, but with separate power supplies 120, the position along theY-axis to be approached by the Y-slide 18 being specified by asuperordinate machine control 122 of the control 118.

A Y-measuring system 124 extending parallel to the Y-axis is providedfor detecting the actual position of the Y-slide. The Y-measuring system124 is seated on the front side 78 of the slide support 20, moreparticularly, between the tool spindle 16 and the main guide 86, andcomprises a position transducer 126 and a position sensor 128, theposition transducer 126 being seated on the slide support 20 and theposition sensor 128 connected to the bridge 70.

The Y-measuring system 124 detects the position of the Y-slide 18relative to the Y-axis and reports it via a line 130 to the control 118.This actual Y-position is compared with the Y-position to be approachedas specified by the machine control 122, which results in a windingcurrent for the respective linear motor 88 and 90, respectively, flowingvia a supply line 132 and 134, respectively, to the respective linearmotor 88 and 90, respectively.

To increase the dynamics of the movement of the Y-slide 18 in thedirection of the Y-axis, the gravity acting on the Y-slide 18 on accountof the mass of the tool spindle 16 and the Y-slide 18 is compensated bya pneumatic counterweight 140 which comprises a pneumatic cylinder 142which is held on the slide support 20 and the piston rod 144 of whichengages the bridge 70 preferably in the region of the tool spindle 16.The pneumatic cylinder 142 is acted upon by pressure in such a way thatit compensates to a considerable extent the gravity acting on theY-slide 18 so that essentially only the acceleration forces have to beapplied by the linear motors 88 and 90.

To enable additional fixing of the Y-slide in defined positions alongthe Y-axis, a brake 150 is also provided between the main guide 84 andthe tool spindle 16. The brake 150 comprises a brake member 152 whichactuates a brake block and, for its part, is held on the bridge 70 and abrake rail 154 which is held on a front side 78 of the slide support 20.

The brake 150 serves to fix the Y-slide 20 when an emergency stop switchis actuated or there is a power failure, and, in the latter case, thebrake 150 is actuated automatically.

The X-slide 26 encompassing the slide support 20 is mounted, for itspart, for displacement on the stand 28 of yoke-type design, moreparticularly, by means of two main guides 170 and 172, each of whichincludes a guide carriage 174 and a guide rail 176. The guide rail 176is seated on a front side 178 of the stand 28, while the guide carriage174 is seated on a rear side 180 of the X-slide 26.

The two main guides 170 and 172 are aligned parallel to the X-axis andextend in spaced relation to one another, preferably in the region oftwo cross beams 184 and 186, respectively, of the yoke-type stand 28forming a slide support.

Two linear motors 190 and 192 are provided for driving the X-slide 26,with their winding plane 194 extending parallel to the X-direction andparallel to the Z-direction. The two linear motors 190 and 192 likewiselie alongside the cross beams 184 and 186, with the lower linear motor190 located below the lower cross beam 184 and the upper linear motor192 located above the upper cross beam 186.

Each of the linear motors 190 and 192 includes a primary part 198carried by a holding flange 196 arranged on the X-slide 26. Opposite theprimary part 198 is a secondary part 200 which, for its part, is held bya supporting element 202 which is arranged on a side face 204 of thecross beams 184 and 186, respectively. The holding flange 196 likewiseoverlaps the side face 204 of the respective cross beam 184 and 186,respectively.

Furthermore, an additional guide 206 including a guide carriage 208 anda guide rail 210 is similarly provided for supporting the holding flange196. The guide carriage 208 is held on the holding flange 196 and theguide rail 210 on the respective cross beam 184 and 186, respectively.The additional guide 206 likewise engages an end of the respectiveholding flange 196 facing away from the X-slide 26 so that therespective linear motor 190 and 192, respectively, lies between theadditional guide 206 and the respective main guide 170 and 172,respectively, and the primary part 198 is supported on both sides withrespect to the secondary part 200 by the respective additional guide 206and the respective main guide 170 and 172, respectively.

In the same way as described in connection with the linear motors 88 and90, respectively, the holding flange 196 is provided with coolingchannels 212 and the supporting element 202 with cooling channels 214through which there flows coolant which is cooled down to a definedtemperature by the cooling device.

Two controls 220 and 222, each with an associated power supply of theirown for the respective linear motors 190 and 192, respectively, areprovided for operating the two linear motors 190 and 192. The controls220 and 222 supply the linear motors 190 and 192 with power via supplylines 224 and 226, respectively, with the position along the X-axisbeing specified by the super-ordinate machine control 122.

Two measuring systems 228 and 230 are provided for detecting the exactX-position of the X-slide 26 along the X-axis. The measuring system 228is located close to the linear motor 190, preferably on the side thereoffacing away from the stand 28 and the measuring system 230 close to thelinear motor 192, preferably on the side thereof facing away from thecross beam 186.

Each of the two measuring systems 228 and 230, respectively, includes aposition transducer 232 and a position sensor 234, the positiontransducer 232 being connected to the stand 28 and the position sensor234 to the X-slide 26.

Associated with the control 220 for the linear motor 190 is themeasuring system 228 which is located close to the latter, andassociated with the control 222 for the linear motor 192 is themeasuring system 230.

Owing to the large distance between the linear motors 190 and 192 in thedirection of the Y-axis and hence also to the large distance between themeasuring systems 228 and 230, the association of a respective measuringsystem of its own with each of the controls 220 and 222 serves to allowthese two controls 220 and 222 to operate completely independently ofone another as two separate NC-axis controls, but simultaneously, sothat each linear motor 190 and 192, respectively, approaches in acontrolled manner the X-position specified by the machine control 222 inaccordance with the respective actual measured values of the associatedmeasuring system 228 and 230, respectively. In this way, active parallelguidance of the X-slide 26, more particularly, parallel to the Y-axis,is achievable and so the parallel alignment of the X-slide 26 with theY-axis is carried out in an actively controlled way.

Two brakes 250 and 252 are additionally provided for fixing the X-slide26 in positions along the X-axis. Each of these comprises a brake member254 with brake blocks and a brake rail 256, with the brake rail 256 ofthe brake 250 being held on the cross beam 184 and the brake rail of thebrake 252 on the cross beam 186, while the brake members 254 of the twobrakes 250 and 252 are seated on the rear side 180 of the X-slide 26.

Both brakes 250 and 252 are provided for fixing the X-slide when anemergency stop switch is actuated or a power failure occurs.

The longitudinal bed 34 comprises two supporting beams 290 and 292extending in spaced relation to one another and parallel to the Z-axis.These form a slide support and carry main guides 294 and 296,respectively, for the Z-slide 42. Each of the main guides has a guiderail 298 resting on the supporting beam 290 and 292, respectively, and aguide carriage 300 displaceable on the guide rail 298 and held on theZ-slide 42.

The Z-slide 42 includes a housing 302 of the rotary drive 44 on which arotor designated in its entirety 304 is mounted by means of a rotarybearing 306 for rotation about the B-axis.

The rotor 306 is driven directly by a motor designated in its entirety308, the stator part 310 of which is mounted in the housing 302 and therotor part 312 of which is seated rotatably on the rotor, the statorpart 310 and the rotor part 312 being arranged between the rotarybearing 306 and the guide carriage 300 in the housing 302.

A rotary encoder 314 is arranged radially within the motor 308 fordetecting the rotary positions of the rotor 304 relative to the housing302. This rotary encoder 314 reports the actual rotary position of therotor 304 relative to the housing 302 to a control 316 which, for itspart, supplies the motor 308 with power via a supply line so that therotary movements can be carried out as NC-controlled B-axis movements.

The individual rotary positions of the motor 308 are transmitted to thecontrol 316 for the axis of rotation via the machine control 122.

The support 46 is provided on the rotor 304 for fixing the workpieceholder and has roller bearings 320 arranged in spaced relation to oneanother for supporting the workpiece holder on an underside 322.Furthermore, the roller bearings 320 engage grooves 324 of the workpieceholder so that by movement of the support 46 in the direction towardsthe housing 302, the workpiece holder can likewise be acted upon in thisdirection and positioned on rests 326 on the rotor 304. These rests 326serve to center and precisely align the workpiece holder 48 relative tothe rotor 304 to achieve exact positioning of the workpiece holder 48relative to the rotor 304 and hence with respect to the B-axis and theZ-axis. The rests 326 preferably form bearing surfaces extendingtransversely to the B-axis and also include centering bolts 330 whichengage corresponding centering bores 332 on the workpiece holder 48 toposition the latter in a defined manner with respect to the B-axis onthe rotor 304.

To move the support 46 towards the housing 302 or away from the latter,a top part of the rotor 304 is provided with a piston 334 which is heldon the housing 302 and on which a cylinder 336 enclosed by the rotor 304is guided for movement in the direction of the axis of rotation orB-axis. This cylinder 336 carries the support 46 with the rollerbearings 320 and is displaceable by cylinder chambers 335a or 335b beingacted upon with hydraulic medium.

The cylinder chambers 335a and 335b in the rotor 304 are supplied by acentral, stationary feeder 338 extending through a piston rod of thepiston 334. The feeder 338 extends from the housing 302 into the rotor304 and at the level of the cylinder chambers 335a and 335b connects thecylinder chambers 335a and 335b to their hydraulic channels via rotaryfeeders.

A brake 340 is additionally provided for fixing the rotor 304 relativeto the housing 302. The brake 340 comprises a brake member 342 and abrake flange 344, the brake flange 344 being rigidly connected to therotor 304 and the brake member 342 being firmly seated on the housing302.

With the brake 340 the rotary position of the workpiece 12 seated on theworkpiece holder 48 is fixable for machining by the tool 14.

Two linear motors 360 and 362 are provided for displacing the Z-slide 42along the Z-axis. Their winding planes 364 extend in a plane parallel tothe Z- and Y-axes. The two linear motors 360 and 362 lie alongside thesupporting beams in the region of side faces 366 facing away from oneanother.

Each of the linear motors 360 and 362 includes a primary part 368 whichis held on a holding flange 370. The holding flange 370 is held, for itspart, on the Z-slide and extends alongside the supporting beams 290 and292, thereby overlapping their side faces 366. Arranged opposite theprimary part 368 is a secondary part 372 which, for its part, is seatedon a supporting element 374 which, in turn, is held on the respectiveside face 366.

Cooling channels 371 and 375, respectively, are also provided in theholding flange 370 and in the supporting element 374, with coolantflowing through them in the same way as for the X-axis or the Y-axis.

In the same way as for the Y-axis and the X-axis, the holding flange 370is supported by an additional guide designated in its entirety 376 whichcomprises a guide carriage 378 and a guide rail 380, the guide rail 380being connected to the respective supporting beam 290 and 292,respectively, and the guide carriage 380 being rigidly held on theholding flange 370.

The forces acting between the primary part 368 and the secondary part372 are thus absorbed in the same way as for the Y-axis and the X-axisby the respective main guide 294 and 296, respectively, and thecorresponding additional guide 376.

Brakes 381 and 383 are additionally provided for fixing the Z-slide 42.These preferably act between the longitudinal bed 34 and the holdingflanges 370 and are constructed in the same way as brakes 250 and 252.

A measuring system 384 and 386, respectively, is associated with each ofthe linear motors 360 and 362 for detecting the movement of the Z-slide42 along the Z-axis. The measuring systems are arranged on an inner side388 and 390, respectively, of the respective supporting beams 290 and292, respectively, in order to lie as close as possible to therespective linear motor 360 and 362, respectively.

Each of the measuring systems 384 and 386 comprises a positiontransducer 392 fixedly connected to the longitudinal bed 34 and aposition sensor 394 connected to the Z-slide 42.

A control 396 and 398, respectively, is associated with each of the twolinear motors 360 and 362 for operating these, and associated with eachof these controls 396 and 398, respectively, is a position measuringsystem 384 and 386, respectively, for detecting the actual position inthe Z-direction. The position to be driven to along the Z-axis istransmitted by the machine control 122 to the two controls 396 and 398which then compare this with the actual positions detected by themeasuring systems 384 and 386.

Both controls 396 and 398 operate independently of one another so thatan active parallel alignment of the Z-slide relative to the X-axis canthereby be carried out exactly as described in connection with thecontrols 220 and 222.

In a second embodiment of an inventive machining center, illustrated inFIG. 6, a work area 400, for example, for the solution according to thefirst embodiment, in which machining of the workpiece 12 is carried outby the tool 14, is enclosed by a cell 402 which comprises a front wall404 standing essentially vertical and parallel to the XY-plane andarranged opposite the tool spindle 16. The workpiece holder 48 isdisplaceable along the Z-axis between the front wall 404 and the Y-slide18. The cell 402, furthermore, comprises two side walls 406 and 408which are arranged in spaced relation to one another and between whichthe Z-slide designated in its entirety 42 is displaceable. These sidewalls 406 and 408 extend from the front wall 404 in the directiontowards the Y-slide 18 which is displaceable in both the Y- andX-directions with the tool spindle 16.

A rear end of the cell 402 opposite the front wall 404 is formed by twoshields 410 and 412 which are held on the X-slide 26 and extend from amovement gap 414 extending in the Y-direction for the tool spindle 16,more particularly, to such an extent in the X-direction that they reston both sides and in all X-positions of the X-slide 26 against rear sideedges 416 and 418, respectively, of the side walls 406 and 408,respectively, or project over these in the X-direction on a side facingthe work area 400.

The two shields 410 and 412 are rigidly held on the X-slide 26 via alinkage, not illustrated in the drawings, and form a partly rearward endof the cell 402.

This end is supplemented by a top cover 420 in the form of a shield forclosing off the movement gap 414 above the tool spindle 16 and a bottomcover 422 for closing off the movement gap 414 below the tool spindle16.

As illustrated in FIG. 7, the top cover 420 is a plate which is held onthe Y-slide 18 and is guided in grooves 424 and 426 of edge rails 428and 430 delimiting the movement gap 414 and extending in theY-direction. The extent of the plate 420 is selected such that itterminates with a top edge 432 in all Y-positions of the tool spindle 16at a top edge 434 of the shields 410 and 412 or projects upwards overthese.

The bottom cover 422, on the other hand, is a so-called telescope-typecover, as illustrated in FIG. 8, which comprises a plurality of coverplates 440 which overlap one another like a telescope and are pushableover one another. The cover plates 440 are guided in a plurality ofgrooves 442 and 444, respectively, lying one behind the other in theZ-direction in the edge rails 428 and 430, respectively. The top one ofthe cover plates 440 is held on the Z-slide, while the bottom one of thecover plates 440 is connected to a bottom part 450 of the cell 402, withthe bottom part 450 forming a bottom end of the cell 402.

As illustrated in FIGS. 7 and 8, the two shields 410 and 412 arelight-weight building panels which comprise two outer sheets 411extending parallel to one another and a corrugated inner sheet 413connected between these and to these, preferably adhesively, eachconsisting of thin sheet metal, preferably aluminum sheet metal.

Furthermore, each of the side walls 406 and 408 is provided with a door452 and 454, respectively, for supplying the work area 40 with aworkpiece holder 48.

The respective door is located above a transportation track 456 for theworkpiece holder 48, with the transportation track 456 extending at adistance from the Y-slide 18 and from a machining position 458 of theworkpiece 14 parallel to the X-direction through the cell 402.

Also arranged outside of the cell 402 is a tool magazine designated inits entirety 460 and comprising a magazine wheel 464 rotatable about anaxis 462, with the axis 462 preferably extending parallel to the spindleaxis 52. Arranged on the circumference of this magazine wheel 464 arereceptacles 466 for a plurality of tools.

The magazine wheel 464 is arranged in such a way that a transferposition 468 lies within the Y/X-range of displacement of the toolspindle 16 so that the tool spindle 16 can drive directly with the tool14 into the transfer position 468 owing to its moveability in theY/X-plane.

For this purpose there is provided in the rear region of the side wall406 adjoining the rear edge 416 a double-swing door 470 which isillustrated in detail in FIG. 9. The double-swing door 470 comprises twodoor leaves 476 and 478, respectively, mounted on the side wall 406 forpivoting movement about axes 472 and 474, respectively, parallel to theZ-axis. In a closed state, the door leaves 476 and 478 have front edges480 and 482, respectively, standing at a short distance from one anotherso that the cell 402 is closed when the double-swing door 470 is in theclosed state. These door leaves 476 and 478 are acted upon in thedirection of their closed position by two spring elements 484 and 486,the closed position being fixed by two stops 488 and 490, respectively,against which the spring elements 484 and 486 place two pivot arms 492and 494, respectively, with the spring elements 484 and 486 preferablyengaging the pivot arms.

Opening of the double-swing door 470 is brought about by the toolspindle 16 being driven into a defined Y-position 496 and then in theX-direction against the door leaves 476 and 478, for which purpose thedoor leaves 476 and 478 are preferably provided with damping elements498 and 500, respectively, in the region of their front edges 480 and482, respectively. The tool spindle 16 thus pushes with its externalhousing 502 each of the door leaves 476 and 478 into an open positionillustrated in dot-and-dash lines in FIG. 9, moves into the transferposition 468, transfers the tool 14 and after rotation of the magazinewheel 464, removes a new tool 14 from the transfer position 468. In thetransfer position 468 (illustrated by a dot-and-dash line) the toolspindle 16 stands such that its external housing 502 holds the doorleaves 476 and 478 in the open position.

Each of the door leaves 476 and 478 is additionally provided with afriction brake 504 which comprises a friction wheel 506 which is fixedlyconnected to the respective door leaf 476 and 478, respectively, and,for its part, rests against a friction block 508 which is urged by aspring-elastic element 510 against the friction wheel 506. This preventsthe two door leaves 476 and 478 from striking back in the direction oftheir closed position when opened quickly and also thereby ensures slowclosing of the door leaves 476 and 478.

The present disclosure relates to the subject matter disclosed in Germanapplication No. P 43 07 482.0 of May 1, 1992, the entire specificationof which is incorporated herein by reference.

What is claimed is:
 1. A machine tool comprising:(a) a frame; (b) aworkpiece holder on said frame for receiving a workpiece to be machined;(c) at least one slide mounted on said frame for movement with respectto said frame in the direction of at least one axis; (d) a tool holdermounted on said slide for receiving a tool for machining a workpiece;(e) a drive for moving said slide along said at least one axis, saiddrive including a first and second electric linear motor each alignedparallel to said at least one axis and spaced apart with at least partof said slide extending between said linear motors; (f) a control systemfor controlling the movement of said slide along said axis; wherein saidcontrol system comprises a first control unit for operating said firstlinear motor as an independent NC axis and a second control unit foroperating said second linear motor as an independent NC axis wherebyeach motor is capable of being operated independently of the other, butsimultaneously and with parallel displacement along said axis; and (g) aslide support for supporting said slide, said slide support having atleast two sides and a front face having a geometric center, and whereinsaid motors are respectively arranged on said at least two sides of saidslide support, so that transverse to the direction of said at least oneaxis, said motors are in outer regions of said slide and said slidesupport with respect to said front face center.
 2. The machine tool asin claim 1 further comprising first and second position measuringsystems respectively associated with said first and said second motors.3. The machine tool as in claim 1 further comprising a brake for saidslide.
 4. The machine tool as in claim 1 wherein said motors arearranged on opposite outer sides of said slide support.
 5. The machinetool as in claim 1 further comprising cooling means for at least one ofsaid linear motors.
 6. The machine tool as in claim 5 wherein saidcooling means comprises a holding element for said at least one of saidlinear motors, said holding element having cooling channels.
 7. Themachine tool as in claim 6 wherein said cooling channels are coolable byflow of a coolant coolable by a cooling device.
 8. A machine toolcomprising:(a) a frame; (b) a first slide moveable with respect to saidframe in the direction of at least one axis; (c) a tool spindle mountedon said first slide for receiving a tool for machining a workpiece; (d)a first slide support mounted on said frame and bearing said firstslide, said first slide support being shaped as a yoke having a centralopening through which said tool spindle extends; and (e) a drive formoving said first slide along said at least one axis, said driveincluding a first and second electric linear motor each aligned parallelto said at least one axis and spaced apart with at least part of saidslide extending between said linear motors.
 9. A machine toolcomprising:(a) a frame; (b) a workpiece holder on said frame forreceiving a workpiece to be machined; (c) at least one slide mounted onsaid frame for movement with respect to said frame in the direction ofat least one axis; (d) a tool holder mounted on said slide for receivinga tool for machining a workpiece; (e) a drive for moving said slidealong said at least one axis, said drive including a first and secondelectric linear motor each aligned parallel to said at least one axisand spaced apart with at least part of said slide extending between saidlinear motors; (f) a control unit for controlling the movement of saidslide along said axis; and (g) two braking devices for braking andfixing said slide, said braking devices being spaced apart in adirection transverse to said axis.
 10. The machine tool as in claim 1further comprising a workpiece holder slide retaining said workpieceholder, said workpiece holder slide displaceable in a directiontransverse to said direction of at least one axis.
 11. The machine toolas in claim 1 further comprising a rotary drive for rotating saidworkpiece holder about an axis.
 12. The machine tool as in claims 11wherein said rotary drive comprises a direct drive.
 13. The machine toolas in claim 11 wherein said rotary drive further comprises a brake. 14.The machine tool as in claim 11 wherein said rotary drive comprises arotary table whereby said workpiece holder is rotatable about a verticalaxis.
 15. The machine tool as in claim 14 further comprising means forfixing said workpiece holder on said rotary table and for releasing saidworkpiece holder from said rotary table.
 16. The machine tool as inclaim 1 further comprising a rotary-table slide for retaining a rotarytable and a longitudinal bed in said frame for supporting saidrotary-table slide, said rotary-table slide displaceable on saidlongitudinal bed.
 17. A machine tool comprising:(a) a frame; (b) aworkpiece holder on said frame for receiving a workpiece to be machined;(c) at least one slide mounted on said frame for movement with respectto said frame in the direction of at least one axis; (d) a tool holdermounted on said slide for receiving a tool for machining a workpiece;(e) a drive for moving said slide along said at least one axis, saiddrive including a first and second electric linear motor each alignedparallel to said at least one axis and spaced apart with at least partof said slide extending between said linear motors; (f) a control unitfor controlling the movement of said slide along said axis; (g) at leastone primary guide guiding said slide, said primary guide disposedbetween said motors; and (h) at least one secondary guide guiding saidslide, disposed so that one of said motors lies between said at leastone primary guide and said at least one secondary guide.
 18. A machinetool comprising:(a) a frame; (b) at least one slide mounted on saidframe and being moveable with respect to said frame in the direction ofat least one axis; (c) a drive for moving said slide along said at leastone axis, said drive including a first and second electric linear motoreach aligned parallel to said at least one axis and spaced apart with atleast part of said slide extending between said linear motors; and (d) aslide support for supporting and guiding said slide, said slide supporthaving two opposite sides parallel to said axis with said motorsrespectively being arranged on each of said opposite sides.
 19. Themachine tool as in claim 18 wherein said slide support is shaped as ayoke.
 20. The machine tool as in claim 18 wherein said slide support ispart of a primary slide guided on a primary slide support shaped as ayoke.
 21. A machine tool comprising:(a) a frame; (b) at least one slidemounted on said frame and being moveable with respect to said frame inthe direction of at least one axis; (c) at least one primary guide forguiding said slide; (d) a drive for moving said slide along said atleast one axis, said drive including a first and second electric linearmotor each aligned parallel to said at least one axis and spaced apartwith at least part of said slide and said primary guide extendingbetween said linear motors, each of said motors having a primary portionon a side oriented opposite to said primary guide and a secondaryportion on a side oriented toward said primary guide; and (e) at leastone secondary guide for supporting said primary portion with respect tosaid secondary portion of at least one of said motors.
 22. The machinetool as in claim 21 further comprising control means for operating saidmotors jointly as a single NC axis.
 23. The machine tool as in claim 21further comprising control means for operating each motor independentlyas an NC axis, but simultaneously and with parallel displacement alongsaid axis.
 24. The machine tool as in claim 23 further comprising firstand second position measuring systems respectively associated with saidfirst and said second motors.
 25. The machine tool as in claim 21further comprising a slide support for supporting said slide, said slidesupport having at least two sides and a front face having a geometriccenter, and wherein said motors are respectively arranged on said atleast two sides of said slide support, so that transverse to thedirection of said at least one axis, said motors are in outer regions ofsaid slide and said slide support with respect to said front facecenter.
 26. The machine tool as in claim 25 wherein said motors arearranged on opposite outer sides of said slide support.
 27. The machinetool as in claim 21 further comprising cooling means for at least one ofsaid linear motors.
 28. The machine tool as in claim 27 wherein saidcooling means comprises a holding element for said at least one of saidlinear motors, said holding element having cooling channels.
 29. Themachine tool as in claim 8 further comprising a second slide bearingsaid first slide support and further comprising a second slide supportguiding said second slide, said second slide support being shaped as ayoke having a central opening through which said tool spindle extends.